Bone cement is conventionally prepared directly prior to injection by mixing a bone cement powder, such as poly-methyl-methacrylate (PMMA), a liquid monomer such as methyl-methacrylate monomer (MMA), an x-ray contrast agent, such as barium sulfate, and an activator of the polymerization reaction, such as N,N-dimethyl-p-toluidine to form a fluid mixture. Other additives including but not limited to stabilizers, drugs, fillers, dyes and fibers may also be included in the bone cement. Since the components react upon mixing, immediately leading to polymerization, the components of bone cement are typically kept separate from each other until the user is ready to form the desired bone cement.
Cement leakage is undesired during vertebroplasty and other similar procedures because it can expose patients to serious risks. Accordingly, the viscosity of the cement is an important factor at reducing unwanted leakage. Concomitant with the use of cements of increasing viscosity, however, is the use of high force injection systems. Such high force injection systems may even exceed human physical limits and preclude important tactile force feedback for the surgeon. High viscosity bone cements also may require longer wait times for the composition to reach sufficient viscosity, thereby reducing total work time. Another possible drawback of high viscosity bone cement may be little interdigitation between cement and bone, thereby compromising the mechanical strength of the reinforced bone.
Other examples of bone cement compositions and/or their uses are discussed in U.S. Pat. Nos. 7,138,442; 7,160,932; 7,014,633; 6,752,863; 6,020,396; 5,902,839; 4,910,259; 5,276,070; 5,795,922; 5,650,108; 6,984,063; 4,588,583; 4,902,728; 5,797,873; 6,160,033; US20070027230; EP1850797 and EP 0 701 824, US Pat. Appln. 2007/0032567.
Percutaneous vertebroplasty is one technique utilizing bone cement for treating weakened or collapsed vertebrae and aids in reducing pain induced by diseases such as osteoporosis. In the vertebroplasty procedure, a fractured vertebral body is augmented with a bone cement. The bone cement polymerizes and hardens upon injection into the vertebral body and stabilizes the fracture. Pain relief for the patient is usually immediate and vertebroplasty procedures are characterized by a high rate of success.